Integrated Amplifiers

Seeing an amplifier rated at a mere 35W/8ohm recalls the classic integrateds from Rotel, NAD and, of course, Cambridge itself in the '70s and '80s. In practice Cambridge Audio is more generous and so the AXA35 delivers closer to 2x40W/8ohm and 2x60W/4ohm with sufficient in reserve to support peaks of 51W, 84W, 83W and 60W (or 7.8A) into 8, 4, 2 and 1ohm loads, respectively [10msec, <1% THD – see Graph 1, below]. So this is a beefy enough amplifier for most 88dB+ sensitivity/'8ohm' budget speakers. Overall gain has been reduced to a sensible +36.2dB but the A-wtd S/N ratio is 5-6dB below average at 79dB (re. 0dBW) and the response is slightly 'shaped' with a very gentle roll-off below 100Hz and above 10kHz, amounting to a mere –0.2dB at 20Hz and 20kHz. Distortion is impressively consistent at 0.0016–0.025% across the rated 35W/8ohm power output (20Hz-20kHz).

The partnering AXC35 CD player offers an 'average' 104dB A-wtd S/N from a maximum 2.10V output, while the 930ohm source impedance (rising to 1.06kohm/20Hz) is a little high. THD falls to a modest 0.0019% through bass and mid frequencies over the top 30dB of its dynamic range [black trace, Graph 2], increasing to 0.031% at high (20kHz) frequencies [blue trace]. Jitter is well suppressed at 145psec and the response is flat to within ±0.06dB, 20Hz-20kHz. Cambridge has chosen a hybrid type digital filter offering a modest 58dB stopband rejection but with reduced transient pre-ringing. However, time domain analysis also indicates that the left/right channels are inadvertently offset by one sample period (0.0226msec), possibly through an error in one of the shift registers. PM